Producing resistant varnish coatings on wood



Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE PRODUCING RESISTANTVARNISH INGS N WOOD COAT- Wilhelm Otto Maisch, Stuttgart, Germany, as-

signor to the firm Hermann Frenkel, Molkau,

near, Leipzig, Germany N 0 Drawing.

3 Claims.

cerns modifications of the process described and 5 claimed in my UnitedStates Patent No. 2,114,784.

According to the said patent the wood is coated with aphenol-formaldehyde artificial resin which is hardenable at low ornormal temperatures and then the resin on the wood is hardened at atemperature from normal to near but below 80C. According to a specialmode of carrying outthe process according .to the said patentphenol-formaldehyde artificial resin varnishes are used which areneutralized or slightly acidified by addition of an acid and which dryand harden in the air at ordinary temperatures or in certain cases afterpreliminary hardening are afterhardened in the air at temperatures of40-80 C. These varnish coatings can be improved according to the saidpatent by treating the wood, befpre applying the phenol-formaldehydeartificial resin varnish,'with a pore filler containingphenol-formaldehyde resin which is also hardenable at low or normaltemperatures. The pore filler may also contain fillers and solvents.

I have also already disclosed in the said patent that solutions ofresins, e. g., colophony, shellac, or artificial resins, e. g., vinylresins, may be added to the phenol-formaldehyde resin varnishes, inorder to obtain a better result.

I have now further found that a particularly satisfactory result can beobtained by coating the wood with a varnish consisting of a solution ofan organic solvent and a mixture of. a hardenable phenol-formaldehyderesin obtained by alkali condensing one moi of a phenol with at least1.5 mols of formaldehyde together with an artificial resin from theurea-aldehyde resin group and hardening the resin mixture at atemperature from normal to near but below 80 C. One secures by theaddition of the ureaaldehyde resin 9, more rapid drying of the apmoreparticularly with respect to higher temperatures of -80 C., and also ahigher elasticity and a better stability and resistance against weatherand water. These advantages are surprising; the last-named technicaladvance in particular was in no way to be foreseen. As is well known theurea-aldehyde resins are very sensitive to water, swell in a glue-likemanner under the prolonged action of moisture and can in no case beregarded as resistant to the weather. II This is due to the fact thatthese resins become plied film, superior brightness and light stability,

Application November 17, 1937, Serial No. 175,174

hardened only at about 150 C. and only then are they insoluble in water.All the more surprising therefore is'the property of this resin group ofyielding in combination with phenolformaldehyde resin coatings which areparticu- 6' larly resistant towards water and weather.

A further notable advantage which is secured by mixing a hardenablephenol-formaldehyde resin with an urea-aldehyde resin is that the filmscan be appliedin thicker layers without becoming turbid or opaque.

The hardening of these vresin mixtures takes place with the addition ofan acid hardening agent, such as inorganic or organic acids, at ordinarytemperatures or at temperatures up to about C. Without the addition ofan acid' hardening agent the hardening of the resin mixtures takes placeonly at a temperature of about 80 C.

The urea-aldehyde resins which are used are the products obtained bycondensing i'ormaldehyde with urea or its derivatives, such asmonomethylol-urea or dimethylol-urea, or mixtures of urea and itsderivatives.

The addition of urea-aldehyde resins may amount up to from 5 tocalculated on the phenol-formaldehyde resin. Preferably theureaformaldehyde resins are dissolved in alcohols, more particularlyhigher boiling aliphatic alco-, hols having at least three carbon atoms,or allphatic esters or ketones.

Bummer-Ten kg. of phenol are condensed with 20 kg. of formaldehyde (30%by weight) with an addition of 500 grams or sodium bicarbonate. Theresin is evaporated down in vacuum to the point of thick liquidity andthereupon dissolved in alcohols, esters or ketones. To this solution isadded an urea-formaldehyde resin which has been dissolved in butylalcohol or ethyl alcohol. The urea-formaldehyde resin is added inquantitles of 20% calculated on the phenol-aldehyde resin. The varnishobtained in this way, is applied to wood and dried and hardened attemperatures up to about 80 C. A coating is obtained which is extremelywaterproof and stable towards light.

In place of phenol an equivalent quantity of cresol may be used; Inplace of sodium bicarbonate an equivalent quantity of someother'inorganic or organic base, for instance sodium hydroxide,potassium hydroxide, dimethylamine, may be used.

What I claim is: 1. A process for producing resistant varnish coatingson wood consisting in coating the wood 56 resin from the urea-aldehydewith a varnish consisting ot a solution in an organic solvent of aphenol-formaldehyde resin obtained by alkali condensing one'mol ofphenol with at least 1.5 mols oi iormaldehyde together with anartificial resin group amounting to from 5% to 100% calculated on thephenol-formaldehyde resin and with an acid hardening agent, andhardening the resin mixture in the air at normal temperature.

2. A process for producing resistant varnish coatings on wood consistingin coating the wood with a varnish consisting of a mixture of a solutionin an organic solvent of a mixture of a hardenable phenol-formaldehyderesin obtained by alkali condensing one mol of phenol with at least 1.5mols of formaldehyde together with a solution in an aliphatic alcoholhaving at least three carbon atoms of an artificial resin fromcondensing one moi of phenol the urea-aldehyde resin group amounting tofrom 5% to 100% calculated on the phenol-formaldehvde resin and with anacid hardening agent, and hardening the resin mixture in the air atnormal temperature.

3. A process for producing resistant varnish coatings on wood consistingin coating the wood with a varnish consisting of a solution in anorganic solvent of a mixture of a hardenable phenol-formaldehyde resinobtained by alkali with at least 1.5 mols of formaldehyde together withan artificial resin from the urea-aldehyde resin group in an amount from5 to 100%, calculated on the phenol-formaldehyde resin, and with an acidhardening agent, and hardening the resin mixture in the air at normaltemperature.

WILHELM OTTO MAISCH.

